Becca Winograd-Diaz is Alma's younger sister.
While she and Alma do have some differences and argue from time to time - one reason being Becca feeling like Alma always gets more attention - they are very close and love each other.
In the second season it is revealed, that she - at least in the alternate timeline - too has the same abilities as Jacob and Alma. At first she wants to pretend they don't exits, dismissing them as vivid memories, but in order to find out what is going on with Camila, she starts to use them deliberately - and is in fact very good at it.
Becca and Reed[]
In the first seasons she got engaged to her long-term boyfriend Reed Hollingsworth, who Alma described as "nice". However, shortly after she slept with a bartender and cheated again just a week before her wedding. On her wedding day she confided in Alma about her infidelity, telling her that she doesn't know what is wrong with her and that she freaked out. When she asserts that she does want to marry Reed, Alma tells her not to tell him before the wedding and that she should enjoy the day. Becca listens to Alma and plans to fess up afterwards. After joining her sister in Mexico, she tells Alma she confessed to Reed and that it went terrible: the marriage is going to be annulled.
In the alternate timeline Becca too is married to Reed. On first glance their relationship seems to be less dysfunctional as they appear to be very happy together and trying to get a baby. However, it soon comes out that Becca is actually still on the pill as she's uncertain if she is ready to have a baby and unable to talk about her insecurites to Reed. When Reed finds out, he angrily storms off, telling Becca he's staying at his parents for a while.
After Alma, Becca and Jacob change the timeline again, Becca is no longer together with Reed.